The figures supplied by MS show that most cars can go for around 40 miles (give or take) on empty before the vehicle will be truly empty and you'll be out of juice and stuck.

Is it dangerous to drive with the low fuel light on?

It's not so much dangerous, more that it's just an unnecessary risk. However, if the car was to run out of petrol and break down in the middle of the road that is a potentially dangerous situation. If you're dangerously close to the empty light and in an unfamiliar location, use your satnav or Google Maps act to show you where the nearest petrol stations are.